An infrastructure for supporting roaming communication units in a trunked radio communication system is described in U.S. Pat. No. 4,833,701 issued May 23, 1989, to Richard Comroe et al. (hereinafter "Comroe"), which patent is incorporated herein by this reference. The Comroe invention provides for support of a roaming communication unit that roams from a first trunked communication system to a second (as used herein, "trunked communication system" refers generally to a trunked RF system, including those that offer dispatch and cellular service.). Comroe does not address, however, providing variable communication capabilities for that communication unit as it roams from system to system.
For example, in its home system, it may be appropriate to support a wide variety of communication capabilities for a given communication unit. For example, telephone interconnect for a predefined set of authorized area codes may be desirable. When that communication unit roams to a different communication system, however, such authorization may be inappropriate, notwithstanding the inherent capability of the communication unit to initiate and maintain such a communication, and further notwithstanding the potential capability of the new communication system to support such a communication.
Accordingly, a need exists for an improved roaming support methodology that will readily accommodate controlled variability of communication capabilities that are supported on behalf of a roaming unit.